The gasoline motor is basically an air pump: The more air that flows through it, the more horsepower it makes. If you know how much horsepower your motor makes, you can estimate its air flow in cubic feet per minute CFM. For example, a 1, cc motor in a good state of tune requires about 54 cubic feet per minute to make 78 horsepower.
If you have access to a flow bench, you can measure how much air flow you get through your intake and cylinder head. From this figure, you can calculate horsepower. For example, a stock 1, head flows about 61 CFM. Therefore, the most you could expect with bolt-on modifications would be about 88 horsepower.
Water-Cooled VW Performance Handbook Horsepower and air flow The gasoline motor is basically an air pump: The more air that flows through it, the more horsepower it psx exploit. Estimating air flow by horsepower If you know how much horsepower your motor makes, you can estimate its air flow in cubic feet per minute CFM. VW Book. Oil info.
Oil analysis Engine break-in European oils Disposal Prelubing.Carburetor Size Calculator This is a simple calculator for determining the approximate size of a carburetor. The Volumetric Efficiency is a bit more tricky and is at best a guess unless you have had your engine on the dyno.
Note: These are for normally aspirated engines where the carb does not sit on a blower or otherwise is used on a draw through blown application. These numbers are typically for 4 barrel carburetors. The last bit of confusion is the carburetor type. This selection give a bit more modern approach to the size.
The thinking behind the increase in CFM is that a well prepared race carburetor has a much better fuel atomization and can perform better at lower vacuum ratings then a stock carb so you can use a larger CFM rating. Race carb info from www. As always call an expert at a tuning shop like the above they will give you more information they you will care to know about. The graphs will help you get a visual range on what size you will need.
Open plenum carbs sizes can generally be smaller then a 2 plane manifold. These numbers do not apply to IR type manifolds typical of Weber carbs. Your on your own with them, and good luck and use as a general gauge for sizing your carburetor. Remember, Right Carb, Right Cam, Right Intake and Right Exhaust for your application will be the optimal solution as it's a package that must all work together. Scroll down to view the graphical results!
You can zoom the charts by using your scroll wheel on the mouse or selecting an area of interest on the chart with the mouse. Click areas of interest in the charts to see data points of interest.
Double click in the chart area to reset its view to see all data. All Rights Reserved. Content May NOT be used without written permission. Use at your own risk. Cubic Inches Cubic Centimeter. Stock Modified.Chad Speier Racing Heads. ProFiler v3. Solid ProFiler v. DART v2. Brodix v3. EDE v2. This is probably the most asked question I get.
What size head do I need?? While head CC's are a by-product of a properly sized cylinder head, there are mathematical formulas to lead you to the correct answer. There are many reasons that choosing a cylinder head based off port volume is a bad idea, simply put there are ways to arrive at a port volume! It gives no insight what so ever into the ports velocity profile.
CC's came about in the 60's when the heads where to small so the larger the port, the more power one could make. With three know things about any cylinder head, we can arrive at port volumes. Knowing this along with a program such as Pipemax, we are able to choose cylinder heads in a way they that is proper and logical. It's all about average velocity in the induction, fps is a great starting point! Most cylinder head porters are working off a desired MACH speed of the port.
You can design ports slower than.
How to Calculate Engine CFM Intake
The formula says you need 2. Remember from above, I said you needed to know port volume and average runner length! Again, roof length plus floor length divided by two. Our math is telling us to achieve rpm from a cid, we need 2. The key to any cylinder head is a balanced port. SRH designs and ports based off velocity profiles. Although formulas are nice for "ballpark" sizing, localized and average velocity is KING! Two totally different cylinder heads, different flow curves, different port volumes, but yet the same average airspeed.
Flows All rights reserved.Mon-Thurs 8am - 3pm. Carburetor size and series charts. Your real person source for performance ignition and carburetion tuning.
Need help? Give us a call or a quick Text. This calculator will show you the requirement at WOT, or at the maximum RPM entered, if your Engine is capable of turning RPM but you shift at then use the shift point not the max RPM Big Stall Convertors, huge gears and very light cars are not part of the Calculation and a competent Carburetor Professional should be consulted.
Call Us at for the correct carb for your application. This calculator is designed to give the engine's air intake volume requirements.Cylinder Head Runner Size Selection - Summit Racing Quick Flicks
Enter the designation of displacement, 1 for cubic inches or 2 for cubic centimeters. Enter the engine displacement size for the designation.
Go With the Flow Part I: Making Sense of Cylinder Head Flow Testing
Enter the anticipated maximum safe engine RPMs, typically known as red line. Enter the volumetric efficiency of the engine. Click on Calculate to finalize the calculation; values are updated subsequent to each field change. The value will be returned in Cubic Feet Per Minute required in both the current and optimum volumetric efficiencies VEbased on the entry values you have made.
Basically, the smaller the runner diameter, the less air potential there is. As the runner gets longer, inertia in the column of air will increase the flow at lower rpms and will tend to decrease the flow at higher rpms.
Horsepower and air flow
Once again, inlet port cross-sectional area will be the main determinant of total airflow potential. Calculations for a dynamic running engine are complex as we are dealing with camshafts, exhaust systems, and the larger issue of the cylinder head design.
The calculators on this page will help you plan your attack on cylinder head selection, valve and port sizes and allow you to coordinate your camshaft and exhaust system selection. This page is not designed to answer the questions for turbo or supercharged applications, which is a topic for another day.
Keep in mind that these calculations must be used in conjunction with header tube diameter and length, valve size, head flow, and camshaft selection. For instance, if your camshaft is designed to peak at RPM, but your manifold and headers are tuned for RPM, your actual torque peak will fall somewhere between and RPM, and the useable torque band from to rpm will be lengthened and flattened. On the other hand, if you match the intake, headers, heads, and camshaft all for rpm, the torque peak will fall very close to RPM.
Also, keep in mind that peak torque and peak horsepower do not occur at the same rpm and that when you shift it is always better to fall back to a region of maximum torque instead of trying to "climb the mountain" to get back to your next redline shift point. We cannot emphasize enough that you must view the engine as a complete system and not concentrate on only one aspect of it.
RPM calculated. Target Engine Displacement cubic inches.As used in the automotive context, CFM, or cubic feet per minute, refers to the quantity of air and fuel the fuel delivery system can provide an engine through the intake manifold. Increasing the CFM of the fuel delivery system is commonly done to increase horsepower. However, equipping the engine with a fuel delivery system that provides too much CFM will have the opposite effect. Fortunately, calculating the optimum CFM for a given engine is simple.
Divide the result from Step 1 by 3, Multiply the result from Step 3 by. For example, Therefore, the engine should be equipped with a fuel delivery system capable of providing between and CFM. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Runs, contact us.
Step 2 Divide the result from Step 1 by 3, About the Author This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.We all have heard the statement that an engine is an air pump; the more air it can pump the higher the output will be.
The industry standard for quantifying the amount of air passing through the induction system is a flow bench test. It's commonplace to reference airflow numbers for cylinder heads in conversation and advertisements. The problem is how to decipher this information. If you are like most people, you work under the assumption that more flow is better. But that's not always true. If you ever wanted to understand flow bench testing, read on. And don't forget to check out the next issue for Part II of this story.
Why test for airflow? One of the theories used to make power in an engine is airflow; so then measuring airflow, in theory, should enable one to establish potential output. The performance industry is focused on maximizing an engine's output on an individual component basis. Then documented gains in airflow should produce predictable results in power production. The question could then be posed, why look at airflow and not power?
Whenever designing or modifying components in the induction tract of an engine, the ideal procedure would be to install the part and then dyno check. This would not only be the most accurate, but also the least practical test method. Anyone who has ever ported a cylinder head while quantifying results on a flow bench can only imagine the arduous process of installing the head and running the engine after every port change.
Early on it was recognized that a better method needed to be developed, and that was the flow test. A flow bench allows a quick and easy means of quantifying gains or losses to airflow.
On a dyno, air movement into the engine is registered through an airflow meter, installed in a large funnel-like apparatus referred to as a dyno hat. It attaches to the carburetor or throttle body and measures the total airflow into the engine in terms of volumetric efficiency VEor the amount of charge fill in the bore. Believing that an engine completely fills the bores on every stroke would be incorrect. The swept volume of the cylinder is filled to the greatest capacity during peak torque production.
On most normally aspirated engines a maximum of 85 percent VE is achieved at peak torque. On some very defined race applications, values of percent or slightly above are realized.
Forced induction can raise VE to percent or greater. VE levels of over percent on normally aspirated engines are achieved through intake manifold resonance tuning identified as inertia supercharging: the column of air is moving with such energy that it actually fills the cylinders beyond capacity by compressing the molecules and increasing the air density in the bore. In contrast, the flow bench is a series of vacuum motors and registers airflow by measuring it at a constant pressure.
Test data derived on a flow bench is measured in cubic feet of air per minute CFM.